Why is LSR an Elastomer?
Plastics can be divided into uncross-linked thermoplastics and cross-linked thermosets. The first have intermolecular bonds between the molecule chains, but can move freely relative to their neighbors. They can be melted and solidified multiple times. In contrast, thermosets have “bridges,” or covalent, bonds interconnecting the polymer molecules. Once the material is solidified by chemical curing, it cannot be melted again.
Another class of materials is elastomers, which demonstrate a highly elastic behavior. There are both thermoplastic and thermoset elastomers. Again, the crosslinks in thermoset elastomers are covalent bonds, which are created during the curing or vulcanization process. The molecules of thermoplastic rubbers, on the other hand, are connected by weaker dipole or hydrogen bonds. They are normally copolymers, or a mixture of plastic and rubber, which exhibit both thermoplastic and elastomeric properties. In many cases, thermoplastic and thermoset rubbers may be used interchangeably. However, in demanding applications, thermoset elastomers LSR components are used exclusively because of their better elasticity, resistance to set, and durability.
Examples of thermoset elastomers are Natural Rubber NR (e. g. truck tires), Styrene-Butadiene Rubber SBR (e. g. hoses and profiles), Nitrile-Butadiene Rubber NBR (e. g. sealing) or LSR components, such as Silicone Rubber MQ. Unlike the other elastomers, which have carbon-carbon backbones, LSR components rubbers contain highly flexible siloxane or silicone oxygen backbones; therefore, they have very low glass transition temperatures.
Silicone rubbers have become increasingly popular in a wide variety of industries, therefore their LSR components offer outstanding solutions. This happens mainly because this material maintains its mechanical and electrical properties over a wide range of temperatures. LSR components of Silicone rubbers can be classified according to the polymer employed and the curing process as low-temperature-curing rubbers (RTV – Room Temperature Vulcanization) and high-temperature-curing rubbers (HTV – High Temperature Vulcanization). RTV silicone rubbers come as a soft paste or a viscous liquid. HTV silicone rubbers come in two different physical states: liquid and solid and are therefore called Liquid Silicone Rubbers (LSR) and High Cure Rubbers (HCR).
[1] Gent, A. N.: Engineering with Rubber – How to Design Rubber Components; 2nd edition, Hanser Publishers, Cincinatti, 2001
[2] Ciesielski, A.: An Introduction to Rubber Technology; Smithers Rapra Technology, Shawbury, 1999
[3] Osswald, T. A.; Baur, E.; Brinkmann, S.; Oberbach, K.; Schmachtenberg, E.: International Plastics Handbook; 4th edition, Hanser Gardner Pubilcations, Cincinatti, 2006
[4] Lopez, L., Cogrove, A., Hernandez-Ortiz, J.P. and Osswald, T.A.: Polym. Eng. Sci., vol. 47(5), pp. 675, 2007.
[5] Osswald, T.A. and Hernandez-Ortiz, J.P.: Polymer Processing: Modeling and Simulation, Hanser Publishers, Munich, 2006.
At SIMTEC Silicone Parts, a leading company in manufacturing high precision parts and LSR components, we are exclusively focused and specialized in the production of LSR and LSR/Thermoplastic (Two-Shot) components.
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